Let n be the fraction of structures of size" n which are connected"; e.g., a the fraction of labeled or unlabeled n-vertex graphshavingone component, b the fraction of partitions of n or of an n-set having a single part or block, or c the fraction of n-vertex forests that contain only one tree. Various authors have considered lim n, provided it exists. It is convenient to distinguish three cases depending on the nature of the power series for the structures: purely formal, convergent on the circle of convergence, and other. We determine all possible values for the pair liminf n; limsup n in these cases. Only in
Jason P. Bell, Edward A. Bender, Peter J. Cameron,